In a purely structural sense, the prior trusses of the type discussed have been satisfactory, but their assembly and installation have not been so.
In the interests of production efficiency the practice has grown for trusses to be built in the workshop and then taken to the site ready for installation.
This in-factory production has been successful, largely because it permits the truss parts to be assembled, and the securing of the truss parts to be effected, in a jig ensuring speed and accurate uniformity of truss formation.
Notwithstanding the considerable utility of jigs in truss production, their use has its drawbacks.
In the first place, truss jigs are relatively bulky, and thus present a storage problem. A separate size of jig is required for each truss size or form, unless the jigs are furnished with movable parts; but, even if that be done, a further disability arises because it increases the complexity of the jig design and it involves time-losses in re-locating and re-setting of the jig parts to suit each different truss size or kind. Another shortcoming in the use of jigs is that where (as is usually the case) the joints connecting the truss chords and other members are made (by welding, riveting or otherwise) while the truss assembly is still in the jig; the option to assemble the truss at the workshop or at the site is denied to the builder in the case of trusses too large for convenient transport.